1. Field of Invention. This invention relates to protectors for use in protecting tubular goods employed in the petroleum industry, and, more particularly, to latch-type protectors utilized to protect encapsulated or bare tubing and tool joints of production tubing strings.
2. Background of the Invention. In the petroleum industry, production tubing is disposed within a borehole for transporting oil and gas from subsurface bearing formations to the surface. This tubing is comprised of elongate sections threaded together to form a production string, the joint thereby formed being referred to variously as a tool joint, coupling, or upset.
In conjunction with this production tubing, it is frequently necessary to provide a system for delivering fluid media downhole. One reason may be to permit the injection of chemical treatment fluids near the producing formation for enhancing the production, for treatment of downhole conditions such as those involving undesirable corrosion, salt, or scale, and for delivery of corrosion or scale inhibitors, de-emulsifiers, or the like, downhole.
Yet another reason for providing these fluid delivery systems is for the transmission of fluid pressure to various downhole valves or tools from the surface for purposes of control or the like. Thus, various forms of injection or control lines referred to hereinafter generally as tubing and having internal diameters much smaller than that of the production tubing itself are provided which are disposed radially outward of and adjacent to the production tubing. In some cases the tubing is of an encapsulated variety wherein both the tubing and wire rope (which provides crush resistance from side forces) are encapsulated in an appropriate thermoplastic elastomer, whereas in other applications, the tubing may be of an unencapsulated or bare variety.
In other situations, electrical cables are routed downhole in like manner to the tubing for monitoring pressure instruments or for providing power for downhole motors or the like.
One problem with these tool joints and the associated tubing or cables (referred to hereinafter as tubing for convenience) is that they are frequently subjected to damage from contact with surrounding casing or the formation itself, such as when the production string is moved up or down within the borehole. This damage may be due to abrasion or compressive forces against the joint or tubing which often occurs as the tool joint is moved across a deviation in the borehole. Thus, means were sought for protecting this bare or unencapsulated tubing, cable and the tool joints from damage.
With reference to the accompanying drawings in general, in its most common form this protection took the form of a hollow cylindrically-shaped metallic cover known generally as a tubing protector comprised of half-sections which were disposed circumferentially about the tool joint and the injection or control tubing. These half-sections were hinged longitudinally along diametrically opposed edges by means of two piano-type hinges with mating straight hinge pins. A representative such protector may be seen depicted generally at page 4612 of the 1982-83 Composite Catalog of Oilfield Equipment and Services, published by World Oil.
A plurality of radially inwardly-extending lugs were disposed on the inner surface of the protector at opposed ends which were sized whereby they could form an interference fit contacting the outer surface of the production tubing or sloping portions of the tool joint itself.
These interference fits were intended to prevent relative rotational and longitudinal movement between the protector on the one hand and the production and injection or control tubing. Both such motions were frequently the cause of serious damage to the tool joint and tubing, such as the crimping or crushing of the injection tubing, abrasion of the tool joints, etc.
Although such tubing protectors of various designs afforded some degree of protection, several problems became associated with these protectors. First, the outer diameters of couplings of the commercially available production tubing such as the diameter of the portion of some joints known as the "upset" vary as a function of the specified weight of the production tubing for a given nominal production tubing o.d., the larger sizes of production tubing having greater variations. For example, production tubing having a four inch outer diameter may have tool joints which vary in outer diameter by as much as one inch. However, such widely-ranging variances in outer diameters made the aforementioned critical interference fits difficult to achieve.
One approach to this problem was to fabricate half-sections of protectors of varying sizes. In this manner, half-sections may be paired in relation to the given outer diameter of the given tool joint so as to provide a custom fit. However, such an approach was found to be commerically impractical for several reasons. First, numerous dies of varying radii of curvature had to be maintained for each weight of tubing to provide the desired nominal inner diameters of the tubing protector half-sections to cover the widely varying ranges of outer diameters of the tool joints.
Due to the hinging on both sides of the protector, variation in internal diameters thereof to accommodate different tool joints was provided primarily from the different sizes of protector half-sections which were staked. This approach was found to be prohibitively expensive, resulting in high production costs, large inventory levels, and large amounts of capital tied up in stock in order to accommodate the varying sizes.
Moreover, even for a given specified nominal size of production tubing, manufacturing tolerances, wear on the joints during use, or the like still resulted in oversizing or undersizing of tool joint outer diameters by as much as 0.020-0.030 inches from the specified value. Also the outer diameter of the tubing itself in accordance with conventional industry standard could often typically vary by as much as .+-.0.031 inches or .+-.0.75% for tubing up to 4 inches in diameter or for tubing of 4 inches or more in diameter, respectively. This factor made it not only desirable but often essential to be able to custom fit such protectors at the wellsite to achieve the necessary close interference fit.
Moreover, the outer diameter of the radially outward sloping portion of tool joints also varied with a given weight of production tubing. Thus for a given such weight, it was not uncommon to see in the field substantial variances in length of these portions of the tool joints. This in turn made it difficult to provide for reliable interference fits between these portions and the aforementioned lugs, which is why it was typical in the industry to provide for as much as 0.060-0.080 design clearance between the aforementioned lugs and the production tubing.
This, in turn, meant that it was anticipated that the tubing protector would slide longitudinally along the production tubing until such an interference fit contact between the lugs and the tool joint was effected. Whereas a slight amount of longitudinal displacement of the tubing protector relative to the production tubing was permissible without causing undue wear on the tool joint or tubing, such clearance would at times permit relative rotational movement between the tool joint and the protector. As previously discussed, this frequently resulted in damage to the injection or control tubing and undue wear on the tool joint.
Yet another serious problem encountered in prior tubing protectors was associated with the provision of diametrically opposed piano-type hinges as previously described. In order to effect the necessary tight interference fit, the pins were subjected to inordinately high strains. This was particularly due to the aforementioned impracticability of providing custom fits by means of appropriately sized half-sections alone. Thus installers of the protectors would attempt to make do with the size protector they had on hand, often employing installation or compression tools for compressing the ill-fitting protector sections about the production tubing. This, in turn, frequently resulted in permanent deformation of protector half-sections and hinge pins, thus rendering their removal difficult and their re-installation ill-advised at best and oftentimes impossible.
In summary, tubing protectors were required to fit wide ranges of tubing o.d.s from 3/4 inch to 41/2 inches for example. Even for a specified o.d., it might vary by the aforementioned 0.031 inches or 0.75% or more depending upon where, manufacturer tolerance, and the like. Moreover, for a given tubing o.d., the associated commercially available specified tool joint nominal o.d. also could vary by as much as one inch or more.
Still further, as previously noted, this joint o.d. itself could vary typically by 0.020-0.030 inches due to tolerances, wear, and the like. All of these variations required manufacturers to provide at times as many as 30 different sizes or radius of curvature half-sections of protectors.
Accordingly, due to all of these ranges and dimensional variances, a latch-type production tubing protector was desired which was easy and inexpensive to manufacture, install, and remove, avoided the need for large numbers of dies, inventories of different parts and the like, and yet reliably accommodated a wide variation of tubing and tool joint sizes.